A flat-panel device contains a pair of generally flat plates connected together through an intermediate mechanism to form a relatively thin structure. When used for displaying information, a flat-panel device is typically referred to as a flat-panel display. The two plates are commonly termed the faceplate (or frontplate) and the baseplate (or backplate). The faceplate, which provides the viewing area for the display, is part of a faceplate structure containing one or more layers formed over the faceplate. The baseplate is similarly part of a baseplate structure containing one or more layers formed over the baseplate. The two plate structures are sealed together, typically through an outer wall.
A flat-panel display utilizes various mechanisms such as cathode rays (electrons), plasmas, and liquid crystals to display information on the faceplate. In a flat-panel CRT display, electron-emissive elements are typically provided over the interior surface of the baseplate. Upon being appropriately excited, the electron-emissive elements emit electrons that strike phosphors situated over the interior surface of the faceplate formed with transparent material such as glass. The phosphors then emit light visible on the exterior surface of the faceplate. By appropriately controlling the electron flow, a suitable image is displayed on the faceplate.
For proper display operation, the electron emission needs to occur in a highly evacuated environment, typically a pressure of 10.sup.-7 torr or less for a display of the field-emission type. The two plate structures in a flat-panel CRT display are quite thin. With the enclosure formed by the plate structures and outer wall being at a high vacuum, a pressure differential in the vicinity of 1 atm. is typically present across each plate structure.
Various techniques can be employed to prevent external forces, such as the outside-to-inside pressure differential, from collapsing the display. One conventional technique is to place spacers at suitable locations between the two plate structures. Besides enabling the display to resist external forces, the spacers maintain a fixed spacing between the plate structures.
Unfortunately, special efforts have to be taken in designing a flat-panel display to avoid having the spacers be visible on the viewing area of the faceplate. In addition, the spacers must be inserted carefully between the two plate structures. Usage of spacers thus increases the display manufacturing cost.
Another disadvantage of spacers is that they provide current leakage paths between the two plate structures, leading to increased power consumption. Also, the brightness of a flat-panel CRT display varies directly with the voltage at which the display is operated. That is, the display brightness increases as the operating voltage is increased. Spacers provide voltage breakdown paths that limit the operating voltage, thereby detrimentally affecting the display brightness. For these reasons, it is desirable to eliminate the spacers or, at the minimum, reduce the number needed for a display of given size.
FIGS. 1a-1d (collectively "FIG. 1") illustrate how a field-emission flat-panel CRT display, commonly referred to as a field-emission display ("FED"), is conventionally assembled. As shown in FIG. 1a, the components of the FED include baseplate structure 20, faceplate structure 22, outer wall 24, and multiple spacer walls 26. The FED also has pump-out tube 28 for evacuating the display. Opening 30 extends through baseplate structure 20 at the attachment location for pump-out tube 28.
Display components 20-28 are assembled as depicted in FIG. 1b. Spacers 26 are placed at various locations between plate structures 20 and 22. Pump-out tube 28 is connected to baseplate structure 20 by way of frit (sealing glass) 32 above opening 30. When outer wall 24 consists of frit, wall 24 is sealed directly to plate structures 20 and 22. The sealing of plate structures 20 and 22 is typically performed at a temperature of 450.degree. C. to greater than 600.degree. C.
When the sealing operation is complete, the enclosure formed with plate structures 20 and 22 and outer wall 24 is pumped down to a high vacuum using a vacuum pump 34P of a vacuum pumping system 34 having a tube 34T connected to pump-out tube 28. See FIG. 1c. Subsequent to pump-down, tube 28 is closed with a heating element to seal the display. FIG. 1d shows the sealed FED in which item 28A is the closed remainder of tube 28. Spacer walls 26 are the spacers that it is desirable to reduce in number or eliminate. In so doing, it is desirable that compatibility with a pump-out tube, such as tube 28/28A, be present.